Crosstalk Between Oncoprotein and Chemokine Signaling. The long-term goals of this project are to understand the biochemistry and biology of crosstalk mechanisms between oncoproteins and chemokine signaling pathways in transformed mammalian cells. The Src family kinase Lyn is known to form signaling complexes with the Bcr/Abl oncoprotein in hematopoietic malignant cells. Lyn tyrosine kinase activity is increased in primary blast cells as compared to normal progenitors. However, Lyn's biological and clinical relevance in Bcr/Abl-positive malignancies has not yet been proven. Preliminary data provided in this application support the role of Lyn in crosstalk between Bcr/Abl signaling and SDF-1 chemokine signaling. SDF-1 chemokine normally regulates stem/progenitor cell migration and survival, and is essential for hematopoiesis. We found that Lyn is a target for both Bcr/Abl and a chemokine receptor signaling in malignant progenitors. We hypothesize that since Lyn kinase is stimulated by Bcr/Abl oncoprotein in leukemic stem cells, Bcr/Abl-dependent Lyn activation may mimic and substitute for signals from a chemokine receptor. This results in aberrant, chemokine receptor-independent cell migration and survival. Therefore, we propose these specific aims: 1) Examine crosstalk mechanisms between BCR/ABL signaling and SDF-1 chemokine signaling. The experiments will study mechanism whereby Bcr/Abl de-regulates a chemokine signaling via Lyn and Lyn-associated molecules (PI3K, She, RTKs, RAS-to-MAPK). 2) Analyze mechanisms associated with SDF-1-dependent NF-kappaB activation. The experiments will study mechanisms whereby Bcr/Abl de-regulates Lyn-NF-kappaB signaling axis and determine potential transcriptional cooperativity between NF-kappaB and other transcription factors in Bcr/Abl-dependent malignancies. 3) Utilize the anti-Lyn small interfering RNA (siRNA) and other Lyn inhibitors to determine the potential of Lyn as a valid drug target in Bcr/Abl-dependent malignant cell movement and survival. Our preliminary results, based on the use of anti-Lyn siRNA, indicate that in Bcr/Abl-positive cells there is an over-reliance on the Lyn signal transduction pathways as compared to normal progenitors. We still do not know the molecular/biochemical mechanism of such over-reliance and we intend to study this in this project. Accordingly, knockdown of Lyn (and Lyn-associated pathological crosstalk mechanism described in the Specific Aims 1-2) might constitute a unique strategy for the selective elimination of Bcr/Abl positive cells in hematological malignancies. The analogous Src kinases-targeted strategy may have application to solid tumors.